class Test {
    private static int count = 0;

    public void add() {
        synchronized(this) {
            count++;
        }
    }

    public int getCount() {
        return count;
    }
}

public class Demo4 {
    public static void main(String[] args) throws InterruptedException {
        Test test = new Test();
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                test.add();
            }
        });

        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                test.add();
            }
        });

        t1.start();
        t2.start();
        t1.join();;
        t2.join();

        System.out.println("count = " + test.getCount());
    }
}
